Patent GB-964183-A (GB)
Title: Improvements in the manufacture of nitrotoluenes
IPC: C07C205/06
Filed: 1961-12-04
Abstract: <PICT:0964183/C1/1> A countercurrent process for the production of dinitrotoluene, trinitrotoluene or mixtures of these compounds which comprises passing toluene through a series of interconnected nitrators each having a separator and simultaneously passing nitrating acid through the series of nitrators in reverse sequence, the reaction mixture leaving each nitrator being fed to its separator in which acid and organic portions are separated and from which the organic portion is fed to the next succeeding nitrator, and the acid portion is fed to the next preceding nitrator, nitrating acid containing nitrous acid being withdrawn from that zone in the series of nitrators where a substantial quantity of dinitrotoluene is present, freed from the major proportion of its content of nitrous acid and then returned to the series of nitrators.  As shown in a series of units consisting of nitrators 1-7, and interconnected separators 8-14, toluene is fed into the first nitrator 1 by a pipe 15, oleum is introduced by means of a pipe 23 in the last nitrator 7 and strong nitric acid is conducted by pipe 17 to nitrators 3-7, the quantities fed to each nitrator being controlled by meters 18-22. The product, which in this case is trinitrotoluene, leaves the separator 14 through pipe 25, and acid leaves the separator 8 through pipe 26.  Toluene introduced into nitrator 1 by means of pipe 15 is partly nitrated to mononitro-toluene in this nitrator and passes in emulsion form to the separator 8 where it is separated as an upper layer and delivered to nitrator 2 where complete nitration to mononitrotoluene takes place.  The mononitrotoluene passes into separator 9 and there flows into nitrator 3 where formation of dinitrotoluene takes place.  In the following nitrators 4-7 further nitration to trinitrotoluene continues successively and the final product leaves the separator 14 through pipe 25.  The nitrating acid, passes in the reverse direction through the series, acids introduced into the last nitrator 7 being separated from the trinitrotoluene in the separator 14 as a bottom layer and flow through pipe 27 to nitrator 6; from separator 13 acids pass to nitrator 5 and so on. Acid leaving separator 10 through pipe 31, is fed by pump 32 into a stripping column 34, where nitrous acid is removed by blowing air through pipe 35 and diluting the charge with 55-60% by weight nitric acid introduced through pipe 37, the nitrous acid being thereby converted into nitrogen oxides. The diluted acid, free from nitrous acid and nitrogen oxides, leaves column 34 and is conducted through pipe 36 to nitrator 2, if desired after being mixed with further dilute nitric acid fed through pipe 42 under control of meter 43. Acid, separated in the separator 9, passes through pipe 44 into nitrator 1 and spent acid from separator 8 leaves the apparatus through pipe 26. During the stripping of nitrous acid in column 34, nitrogen oxides are absorbed in the upper part of the column by the introduced diluted nitric acid and the residual gases escape via pipe 47.  This acid is thus fortified and is withdrawn via pipe 45 by pump 39 and fed via pipe 46 to nitrator 3.